DR DRAKE: One of the main questions that we’re facing with anti-PD-1/anti-PD-L1 is quite simple, exactly how long to treat. So when we first started these trials, they treated for a fixed period — sometimes a year, sometimes 2 years and then would stop. Now some of the trials that are ongoing treat continuously forever.

If patients have an ongoing response and they’re tolerating the drug well, that makes sense. But some of these patients are living a very long time. We’re in the process of preparing a manuscript on some extreme-responding patients who have lived between 4 and actually 8 years on these drugs. So if you’re on continuous drug for 4 to 8 years, that might be a little bit long.

So the question is how long to treat and what’s the best regimen. Really, honestly, there’s 2 critical clinical questions there. So first of all, if a patient has a stable ongoing response, which many do with these drugs, and you stop, how many patients will maintain that response off treatment? We know it’s not zero, actually.

In the paper that Dave McDermott and I published in JCO this year, we showed that there are a fair number of patients who, even on the Phase IB trial, who had long-term responses off treatment, so we know it’s not zero. But we know that from following some of these patients, some of them eventually will relapse.

DR LOVE: Could I just interject, too, you had presented a case actually at the GU symposium of a patient. I think it was the first patient ever treated with nivolumab for renal cell, who got 3 doses of the drug 8 years ago, eventually got into a complete remission and now is still in a complete remission. How do you visualize the pathophysiology? What’s going on with this patient as opposed to every other one?

DR DRAKE: Great question, actually. So there’s 2 or 3 things that we can imagine. One thing is that he was lucky enough to make antitumor T-cells that were both very specific for his tumor and very effective. Also that his tumor metastases that might have been evolving might be a little bit more related to each other and that they might all carry that mutation. So I think that that’s one thing that he might have that other patients haven’t had.

To be honest, we did sequence his tumor. And I can tell you that one thing that was interesting is he didn’t have a ton of mutations. It wasn’t like he had 2 or 3 times as many mutations. So it must have been that he had the lucky mutations that he had a nice response to. And I’ve got to tell you, I mean, honestly, people ask me this all the time: Do you really think that this patient is cured? And I always say, “I certainly hope so.”

But it is possible that what happens is he might have a few tumor cells in his body that his immune system keeps fighting continuously, actually. So we don’t really know that, actually. We can’t see any tumor. We actually scanned him with a complete CT scan. We also did an MRI of the brain to make sure that he had no CNS disease. And he was completely, by those scans, tumor free. And why is this patient like this and other patients are not? We really don’t know right now. We studied him intensively, though.

Bladder cancer

Prostate cancer

Renal cell carcinoma

Checkpoint inhibitors